Smoggy Asian air enters United States

Atmospheric scientists have detected a previously unknown Asian import smuggling its way into the United States. Smoggy air, rich in ozone pollution and other contaminants, sailed clear across the Pacific and then drifted over northwestern states in the spring of 1999.

On April 9, sensors on board an airplane flying off the coast of Washington detected enhanced ozone concentrations between 3,000 and 6,000 meters above sea level. At its worst, the ozone reached 85 parts per billion, reported Daniel Jaffe of the University of Washington at Bothell and his colleagues last month in San Francisco at a meeting of the American Geophysical Union.

A triplet of oxygen atoms, ozone can cause respiratory distress and other health problems, and it can also attack vegetation. The concentration detected by the aircraft is significant, says Jaffe, because the pending federal standard for ozone is an 8-hour average of 80 parts per billion.

Using meteorological data, Jaffe and his colleagues ran models to calculate where the plume of pollution had originated. They traced the dirty air backward across the Pacific to Southeast Asia 5 days earlier.

Whether or not the Asian ozone represents a threat remains unclear. Ground-based sensors throughout the Puget Sound area did not pick up any spike in ozone concentrations at the time the Asian plume was passing overhead, says Naydene Maykut of the Puget Sound Clean Air Agency, nor did an instrument stationed at 1,700 m above sea level in the Cascade mountains.

“It clearly is not of great concern at the moment,” says Maykut. Evidence has indicated that influxes of Asian pollution occur most often in spring, when the Puget Sound area has its cleanest air. “If this [pollution] increases because pollution in the Third World is increasing, it could become something that we need to be more concerned about,” she says.

Jaffe sees the ozone as a more immediate threat. As upper-level air passes over mountains, it mixes with air from the ground, transporting pollution downward. “Potentially, you could see a strong effect from Asia at the Rocky Mountains,” he says.

As this imported air becomes diluted near the ground, however, it becomes harder to detect, he adds. Instead of causing a sudden spike, it may raise the general ozone concentration in an area.

A year ago, Jaffe and other researchers reported finding a cocktail of noxious chemicals coming clear across the Pacific from Asia (SN: 12/12/98, p. 374: At the time, they were using ground-based measurements and did not detect enhanced concentrations of ozone.

More Stories from Science News on Earth